Water treatment device

ABSTRACT

A water treatment device capable of filtering out iron and manganese in raw water by oxidizing them and making them insoluble in water includes a raw water supply tube ( 4 ), one or more jet nozzles ( 5 ), each being at one end portion thereof in communication with the raw water supply tube ( 4 ) and having at the other end thereof a raw water jetting outlet for blowing out the raw water in a jet stream, one or more air introducing tubes ( 6 ) provided in correspondence to the jet nozzle or jet nozzles ( 5 ), each being at one end portion thereof opened to the atmosphere and being at the other end portion thereof opened to the inside of a corresponding one of the jet nozzles ( 5 ) upstream of the raw water jetting outlet and a filter container ( 3 ) containing a filter layer ( 2 ).

TECHNICAL FIELD

[0001] This invention relates to a water treatment device and, moreparticularly, to a water treatment device capable of treating watersoluble substance such as iron and manganese in underground water byoxidizing them and thereby making them insoluble with a simple andcompact device without using an oxidizing agent or a flocculant.

BACKGROUND ART

[0002] Underground water is utilized as raw water for tap water and alsoutilized in industries which require a large quantity of water such asfood, soft drink, beverage, dyestuff industries and also in publicbaths. In these industries, iron and manganese contents contained inunderground water have raised a problem. While iron and manganese aresubstances which are necessary for a human body, contents of thesesubstances exceeding a certain amount give a metal taste to water andturn water to red or black water, thereby making the water unsuitablefor drinking and causing various difficulties in these industries.Further, in a foundation work in building industry, it is indispensableto remove underground water from a foundation site before the foundationwork starts. If a large quantity of iron and manganese is contained inthe underground water, the iron and manganese must be removed from theunderground water before the underground water is discharged to thesewerage because it is legally prohibited to discharge such undergroundwater the sewerage without any treatment.

[0003] In a currently prevailing conventional water treatment device forremoving iron or manganese, an oxidizing agent such, for example, assodium hypochlorite or a flocculant such, for examle, as poly-aluminumchloride (PAC) is added to raw water to oxidize iron or manganese whichis dissolved in the raw water and thereby convert it to iron oxide ormanganese oxide which is insoluble in water and the iron oxide ormanganese oxide is filtered out by filtering the raw water throughfiltering sand.

[0004] In the conventional water treatment device requiring addition ofan oxidizing agent or a flocculant, however, a relatively large amountof oxidizing agent or flocculant is consumed in the device and,therefore, the cost of such oxidizing agent or flocculant is tremendous.

[0005] Further, since hypochlorous acid which is used as the oxidizingagent remains in water after the treatment for oxidizing iron andmanganese, trihalomethane which is a carcinogen is generated and, forremoving trihalomethane, the water must further be filtered through anactivated carbon layer which adds to the cost of the water treatment. Ifprovision of such activated carbon layer is omitted for economic reason,water after filtering must be constantly analyzed for preventinggeneration of trihalomethane caused by addition of an excessive amountof oxidizing agent and, if necessary, the amount of addition of theoxidizing agent must be adjusted. This method requires a high cost ofmaintenance in addition to the cost of purchasing the oxidizing agent.

[0006] Further, the conventional water treatment device generally is acomplex and large-scale system including an aeration tank, aflocculation tank, a precipitation tank, a sand filter tower, an ironand manganese removing tower and a chemical agent tank and this systemrequires a large space for installation. It is impossible to installsuch a large device in a site of a limited space such in a town.

[0007] Furthermore, filtering sand which is used in this water treatmentdevice requiring addition of an oxidizing agent is blocked byaccumulated impurities and therefore must be replaced from time to time.The used sand to be abandoned must be treated as industrial wastebecause it contains a chemical agent and a place where it can beabandoned is extremely restricted by laws and regulations.

[0008] It is, therefore, an object of the present invention to provide awater treatment device capable of treating water soluble substance suchas iron and manganese in underground water by oxidizing them and therebymaking them insoluble with a simple and compact device without using anoxidizing agent or a flocculant.

DISCLOSURE OF THE INVENTION

[0009] For achieving the above described object of the invention, thereis provided a water treatment device comprising a raw water supply tube,one or more jet nozzles, each being at one end portion thereof incommunication with the raw water supply tube and having at the other endportion thereof a raw water jetting outlet for blowing out the raw waterin a jet stream, one or more air introducing tubes provided incorrespondence to said jet nozzle or jet nozzles, each being at one endportion thereof opened to the atmosphere and being at the other endportion thereof opened to the inside of a corresponding one of the jetnozzles upstream of the raw water jetting outlet, a filter containercontaining a filter layer having an upper surface thereof being providedbelow the jet nozzles with a predetermined interval from the raw waterjetting outlets of the jet nozzles, and a filtered water outlet providedin the filter container for taking out water which has been filteredthrough the filter layer.

[0010] According to the invention, by turning raw water to a jet waterstream by means of the jet nozzle which is at one end portion thereof incommunication with the raw water supply tube and introducing air intothe jet nozzle from the air introducing tube which is opened to theinside of the jet nozzle, the jet stream, air is drawn into the jetwater stream and turned to a multiplicity of small air bubbles. The jetwater stream containing the multiplicity of air bubbles is blown out ofthe raw water jetting outlet and is struck against the water surfaceabove the filter layer disposed below the raw water jetting outletthereby causing vehement aeration both in the water above the filterlayer and on the surface of the filter layer. By virtue of thisaeration, soluble substances such as iron and manganese contained in thewater are oxidized and thereby are turned to insoluble substances whichform flocks or precipitates and are caught on the surfaces of grains ofthe filtering material such as filtering sand which constitutes thefilter layer. The filtered water from which the insoluble substances andother foreign matters have been removed by the filter layer is taken outof the filtered water outlet.

[0011] Accordingly, iron, manganese and other insoluble substances inraw water can be made insoluble and can thereby be filtered out with asimple and compact device without using chemicals such as an oxidizingagent or flocculant.

[0012] Further, since the filtered water contains a relatively largeamount of dissolved oxygen as a result of the aeration, by connecting aknown low-speed filtering device to the downstream side of the watertreatment device of the present invention, propagation of aerobic ironbacteria which propagates in the filter layer of the slow-speedfiltering device is enhanced and the iron removal efficiency of thisslow-speed filtering device can thereby be improved.

[0013] Further, according to the invention, space required forinstalling the water treatment device of the present invention mainly isspace for installing the filter container only and, therefore, spacerequired can be much smaller than the space required for installing theconventional water treatment device. Thus, the water treatment device ofthe present invention can be readily installed in a site of a limitedspace in a town.

[0014] Furthermore, in a case where waste filtering sand is abandoned,it is not necessary to deal with it as an industrial waste so that thereis no limitation in a site for abandoning it.

[0015] In one aspect of the invention, there is provided a watertreatment device comprising a raw water supply tube, one or more jetnozzles, each being at one end portion thereof in communication with theraw water supply tube and having at the other end portion thereof a rawwater jetting outlet for blowing out the raw water in a jet stream, oneor more gas introducing tubes provided in correspondence to said jetnozzle or jet nozzles, each being at one end portion thereof connectedto a gas supply source and being at the other end portion thereof openedto the inside of a corresponding one of the jet nozzles upstream of theraw water jetting outlet, a filter container containing a filter layerhaving an upper surface thereof being provided below the jet nozzleswith a predetermined interval from the raw water jetting outlets of thejet nozzles, and a filtered water outlet provided in the filtercontainer for taking out water which has been filtered through thefilter layer.

[0016] According to this aspect of the invention, the gas introducingtube is connected to the gas supply source such as a gas pump or an aircompressor whereby not only air but also other desired gas such, forexample, as nitrogen gas or ozone can be supplied from the gas supplysource. This enables a desired type of gas to be selected in accordancewith the nature of substance to be filtered out. This also enables theflow rate of air or other gas to be controlled to an optimum value forthe filtration.

[0017] As the above described filtering operation is continued, flocksof oxidized substances and other foreign matters are accumulated on thesurface of the filter layer as time elapses with the result that thesurface of the filter layer is dosed with the flocks and other foreignmatters and the filtering function of the filter layer thereby isreduced. In another aspect of the invention, the water treatment devicecomprises means for reciprocating the raw water supply tube in a planeparallel to the surface of the filter layer and, therefore, by operatingthis means in a state where the water surface is adjusted to a levelwhich is slightly above the surface of the filter layer to reciprocatethe raw water supply tube in a plane parallel to the surface of thefilter layer, the jet water stream containing a multiplicity of bubbleswhich is blown out of the raw water jetting outlet is struck vehementlyagainst the surface of the filter layer which is closed with the flocksetc. and, as a result, the entire surface portion of the filter layer isturned over whereby the dosed state of the surface of the filter layerwith the flocks etc. is eliminated and the filtering function of thefilter layer is restored.

[0018] In another aspect of the invention, the water treatment devicefurther comprises a baffle plate provided between the raw water jettingoutlets of the jet nozzles and the surface of the filter layer. The jetwater stream blown out of the raw water jetting outlet of the jet nozzleis agitated further by the baffle plate to enhance the aeration.

[0019] In still another aspect of the invention, the water treatmentdevice further comprises a filter layer support made of a plate screenprovided at the bottom of the filter layer for supporting the filterlayer, a reverse washing tube provided under the filter layer supportfor reverse washing the filter layer, and a reverse washing water outletprovided in the filter container.

[0020] According to this aspect of the invention, when the surface ofthe filter layer is significantly covered with the flocks of theoxidized substances and other foreign matters, supply of raw water tothe filter container is temporarily suspended and reverse washing wateris caused to flow from the reverse washing tube through the filter layersupport upwardly. The flocks and foreign matters covering the surface ofthe filter layer are removed from the surface of the filter layer andare taken out of the reverse washing water outlet. The screen plateserves for causing the reverse washing water to flow in a uniformcounter-stream throughout the filter layer from the bottom surface ofthe filter layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In the accompanying drawings,

[0022]FIG. 1 is a perspective view showing an embodiment of the watertreatment device according to the invention with a part of the side wallof a filter container being removed;

[0023]FIG. 2 is a sectional view showing a jet nozzle and an airintroducing tube in an enlarged scale;

[0024]FIG. 3 is a sectional view showing a mechanism for reciprocating araw water supply tube;

[0025]FIG. 4 is a sectinal view showing a mechanism for guiding the rawwater supply tube;

[0026]FIG. 5 is a perspective view showing another embodiment of thewater treatment device according to the invention; and

[0027]FIG. 6 is a sectional view showing a jet nozzle and a gasintroducing tube of this embodiment in an enlarged scale.

BEST MODE FOR CARRYING OUT THE INVENTION

[0028] Referring now to FIGS. 1 to 4, an embodiment of the inventionwill be described.

[0029] A water treatment device 1 comprises, as its principal elements,a filter container 3 containing a filter layer 2, a raw water supplytube 4, jet nozzles 5 and an air introducing tubes 6.

[0030] The raw water supply tube 4 made of, e.g., a steel pipe, forsupplying raw water to be filtered such as underground water or riverwater to the filter container 3 is connected to a water supply pump 7 bymeans of a rubber hose 8. The water supply pump 7 is provided with rawwater from a water source of the raw water through a water receivingtank, if necessary, and supplies the raw water to the raw water supplytube 4 at a predetermined flow rate.

[0031] The raw water supply tube 4 is disposed above one end portion ofthe filter container 3 in such a manner that the raw water supply tube 4extends in a plane parallel to the surface of the filter layer 2.

[0032] One or more (six in the illustrated example) jet nozzles 5 areprovided in a manner to branch off downward from the raw water supplytube 4. As will be apparent from FIG. 2, the upstream side end portion 5a of each jet nozzle 5 is fitted in the raw water supply tube 4 in sucha manner that the inside of the jet nozzle 5 communicates with the rawwater supply tube 4. In the downstream side end portion of the jetnozzle 5 is formed a raw water jetting outlet 5 b which blows out rawwater in a jet water stream. A preferable inner diameter of the jetnozzle 5 is 3 mm to 6 mm.

[0033] One or more (six in the illustrated example) air introducingtubes 6 are provided, one for each, in the respective jet nozzles 5. Aswill be apparent from FIG. 2, the upstream side end portion 6 a of eachair introducing tube 6 projects obliquely upwardly from the jet nozzle 5with its inside being opened to the atmosphere. The downstream side endportion 6 b is opened to the inside of the jet nozzle 5 upstream of theraw water jetting outlet 5 b. A preferable inner diameter of the airintroducing tube 6 is 2 mm to 4 mm.

[0034] In the filter container 3, the filter layer 2 is provided withits upper surface being disposed below the jet nozzles 5 with apredetermined interval (e.g., about 35 cm) from the raw water jettingoutlets 5 b. The filter layer 2 is made of filtering sand of a uniformgrain size and functions to filter the raw water by catching flocks ofoxidized substances and other foreign matters in the raw water suppliedas a jet stream from the jet nozzles 5. Flow rate of the raw water inthe filter container 3, i.e., the filtering speed, differs dependingupon the degree of filtration of object foreign matter (i.e.,permissible concentration of the foreign matters in the filtered water).For normal filtering of iron and manganese, a filtering speed of 8 cm orbelow per minute is preferable.

[0035] A baffle plate 13 made of, e.g., a steel plate, is providedbetween the raw water jetting outlets 5 b of the jet nozzles 5 and thesurface of the filter layer 2 in such a manner that the baffle plate 13extends in parallel to the raw water supply tube 4 and are disposedbeneath the raw water jetting outlets 5 b. The baffle plate 13 has itsend portions in the longitudinal direction fixed to the inside wallsurfaces of side walls 3 a and 3 b by means of, e.g., welding. By way ofexample, if the depth of water from the surface of water of the filtercontainer 3 to the surface of the filter layer 2 is 30 cm and distancebetween the raw water jetting outlet 5 b of the jet nozzle 5 to thesurface of the water is 5 cm, a preferable depth of the baffle plate 13from the surface of the water is about 5 cm (i.e., distance from the rawwater jetting outlet 5 b is about 10 cm).

[0036] A filter layer support 14 made of a plate screen (a wedge-wirescreen in the illustrated example) is provided at a predetermined heightfrom the bottom of the filter container 3 for supporting the filterlayer 2 in its entirety. In the illustrated example, the wedge-wirescreen is so disposed that it supports the filter layer 2 with its flatsurface 14 a and the width of slits 14 b of the wedge-wire screenincreases toward the lower end thereof. A reverse washing tube 15 isprovided in a lower space 16 of the filter container 3 under the filterlayer support 14 for reverse washing the filter layer 2. The reversewashing tube 15 is formed with a plurality of reverse washing waterjetting outlets 15 a opening toward the filter layer support 14. Thereverse washing tube 15 is connected to an unillustrated reverse washingwater supply source.

[0037] A pump may be provided downstream of the filter layer 2 so thatwater is sucked compulsorily by the pump for enhancing filteringefficiency.

[0038] By supporting the filter layer 2 by the filter layer support 14made of a plate screen, a support structure made of generally three sandlayers of sand, i.e., sand of a small grain, sand of a middle grain andsand of a large grain in the order from the top to the bottom which isrequired in the conventional water treatment device can be eliminatedand, therefore, the design of the filter container can be simplified.

[0039] A filtered water outlet 17 for taking out water which has beenfiltered through the filter layer 2 is provided in a side wall 3 c ofthe filter container 3 facing the lower space 16 of the filter container3. In one end portion of the filter container 3 (in the right endportion in the illustrated example) is provided an overflow trough 18with its upper edges being located slightly above the surface of thefilter layer 2. One end of the overflow trough 18 is closed with a sidewall 3 b of the filter container 3 and the other end of the overflowtrough 18 is dosed with a cover 19. The cover 19 of the overflow trough18 is dosed when raw water is filtered and is opened during reversewashing to function as a reverse washing water outlet.

[0040] As the reverse washing device, a known device such, for example,as a device which starts the reverse washing operation automaticallyupon detecting that the water level of the filter container 3 hasexceeded a predetermined level may be employed.

[0041] In the present embodiment, a raw water supply tube reciprocatingmechanism 20 for reciprocating the raw water supply tube 4 in a planeparallel to the surface of the filter layer 2 is comprised of a screwbox 21, a feed screw 22, a feed screw drive device 23 including anelectric motor and reduction gear for driving the feed screw 22. Thefeed screw drive device 23 is fixed to a side wall 3 d of the filtercontainer 3. As shown in FIG. 3 in an enlarged scale, the screw box 21is formed in its central portion with a screw hole 21 a and is fixed tothe raw water supply tube 4 with mounting members 24 which are fixed tothe tube 4 by proper means such as welding in such a manner that theaxial direction of the screw hole 21 a crosses the axial direction ofthe raw water supply tube 4.

[0042] The feed screw 22 which is in threaded engagement with the screwhole 21 a of the screw box 21 extends in a direction crossing the rawwater supply tube 4 and is supported by bearings 25 and 26 which aresecured to the side walls 3 c and 3 d of the filter container 3. The endportion of the feed screw 22 on the side of the side wall 3 d extendsthrough the side wall 3 d to the outside of the filter container 3 andis connected to a feed screw drive device 23 so that the feed screw 22is driven and rotated by the feed screw drive device 23. Accordingly, byoperating the feed screw drive device 23, the feed screw 22 is rotatedand the raw water supply tube 4 fixed to the screw box 21 thereby ismoved in the direction of arrow A in FIG. 3. When the electric motor ofthe feed screw drive device 23 is reversely rotated, the raw watersupply tube 4 is moved in the direction of arrow B in FIG. 3.

[0043] For performing the reciprocating motion of the raw water supplytube 4 in a smooth and stable manner, in the present embodiment, rollers28 are secured to the raw water supply tube 4 by means of mountingmembers 27 in locations on the side walls 3 a and 3 b of the filtercontainer 3 as shown in FIG. 4 in an enlarged scale and the side walls 3a and 3 b are formed in their upper end portion with guide grooves 29 inwhich the rotating rollers 28 are guided. For performing thereciprocating movement of the raw water supply tube 4 in a stablemanner, other means may be employed such as a couple of feed screws.

[0044] The operation of the water treatment device of the abovedescribed embodiment will now be described.

[0045] During filtering of raw water, raw water is supplied from thewater supply pump 7 to the jet nozzles 5 through the raw water supplytube 4 while the depth of water above the surface of the filter layer 2is maintained, e.g., at 30 cm. The raw water is caused to flow in a jetwater stream by setting the flow rate of water in the jet nozzles 5 at,e.g., 1.5 l/min. to 3 l/min. while air is drawn into the jet nozzles 5from the air introducing tubes 6 opening to the inside of the jetnozzles 5 at a flow rate of, e.g., 0.5 l/min. to 1 l/min. The air isdrawn into the jet water stream in a multiplicity of small air bubblesand the jet water stream containing the air bubbles is blown out of theraw water jetting outlets 5 b of the jet nozzles 5 and is struck againstthe water surface of the filter layer 2 thereby causing vehementaeration on the water surface and on the filter layer 2. The baffleplate 13 enhances this aeration. By virtue of this aeration, solublesubstances such as iron and manganese are oxidized and thereby areturned to insoluble substances which form flocks or precipitates and arecaught on the surfaces of the grains of the filtering sand whichconstitutes the filter layer 2. The filtered water from which theinsoluble substances and other foreign matters have been removed by thefilter layer 2 is taken out of the filtered water outlet 17.

[0046] As the above described filtering operation is continued, flocksof oxidized substances and other foreign matters are accumulated on thesurface of the filter layer 2 as time elapses. The surface of the filterlayer 2 is covered and closed with these flocks and foreign matters and,as a result, the filtering function of the filter layer 2 is reduced.

[0047] In this case, as shown in FIG. 3, while the raw water and air aresupplied with the water level being adjusted at a level of, e.g., 10 cmabove the surface of the filter layer 2, the raw water supply tubereciprocating mechanism 20 is actuated to reciprocate the raw watersupply tube 4 in a plane parallel to the surface of the filter layer 2.Since, by this operation, a jet water stream containing a multiplicityof air bubbles which is blown out of the raw water jetting outlets 5 bis struck vehemently against the closed surface of the filter layer 2,the entire surface of the filter layer 2 is turned over whereby thedosed state of the surface of the filter layer 2 is eliminated and thefilter layer 2 restores its filtering function.

[0048] When flocks of oxidized substances and other foreign matters areaccumulated on the surface of the filter layer 2 to such an extent thatthe turning over of the surface of the filter layer 2 by actuation ofthe raw water supply tube reciprocating mechanism 20 is not sufficientfor restoring the filtering function completely, supply of raw water tothe filter container 3 is temporarily suspended to reduce the waterlevel on the surface of the filter layer 2 to zero, the cover 19 of theoverflow trough 18 forming the reverse washing water outlet is openedand reverse washing water is caused to flow upwardly from the reversewashing water tube 15 through the filter layer support 14. The flocksand foregin matters covering the filter layer 2 thereby are removed andtaken out of the reverse washing water outlet 19.

[0049] In the above described embodiment, the raw water supply tubereciprocating mechanism 20 is formed with a feed screw mechanism. Theraw water supply tube reciprocating mechanism is not limited to this butmay be composed of other means such as chain drive.

[0050] By way of an actual example, the above described embodiment ofthe invention was used to filter underground water collected in SanoCity, Tochigi Prefecture, Japan. Change in the concentrations of ironand manganese in the underground water is shown in Table 1. TABLE 1before filtering (mg/l) after filtering (mg/l) iron 18 0.6 manganese 2.01.7

[0051] Referring to FIGS. 5 and 6, another embodiment of the inventionwill be described. In this embodiment, the same component parts as thosein the previously described embodiment are shown by the same referencecharacters and description thereof will be omitted.

[0052] A water treatment device 1 comprises, as main component parts, afilter container 3 including a filter layer 2, a raw water supply tube4, jet nozzles 5 and gas introducing tubes 36.

[0053] The raw water supply tube 4 made, e.g., of a steel tube, forsupplying raw water to be filtered such as underground water or riverwater is connected to a water supply pump 7 through a rubber hose 8. Thewater supply pump 7 is provided with raw water from a water source ofthe raw water through a water receiving tank, if necessary, and suppliesthe raw water to the raw water supply tube 4 at a predetermined flowrate.

[0054] One or more (six in the illustrated example) jet nozzles 5 areprovided in a manner to branch off downwardly from the raw water supplytube 4.

[0055] A gas supply tube 9 extends in parallel to the raw water supplytube 4 in a plane above the filter container 3 and is fixed to the rawwater supply tube 4 by means of mounting members 10. The gas supply tube9 is connected by means of a rubber hose 11 to an air supply source 12such as an air pump or an air compressor which supplies air or a gassupply source 12 which supplies gas such as a nitrogen gas or ozone.

[0056] One or more (six in the illustrated example) gas introducingtubes 36 are provided in a manner to branch off from the gas supply tube9. As will be apparent from FIG. 6, the upstream side end portion 36 aof each gas introducing tube 36 is fitted in the gas supply tube 9 insuch a manner that the inside of the gas introducing tube 36communicates with the gas supply tube 9 and the downstream side endportion 36 b of the gas introducing tube 36 is opened to the inside ofthe jet nozzle 5 upstream of the raw water jetting outlet 5 b. Apreferable inner diameter of the gas introducing tube 36 is 2 mm to 4mm.

[0057] In this embodiment, the gas supply tube and the gas introducingtubes are provided outside of the raw water supply tube and the jetnozzles. Alternatively, the gas supply tube and the jet nozzles may beprovide inside of the raw water supply tube and the jet nozzles.

[0058] According to ths embodiment, not only air but also a desired gassuch as nitrogen gas or ozone can be supplyed from the gas supply sourceso that an optimum gas may be selected in accordance with the nature ofthe substance to be filtered out. Further, the flow rate of air or othergas may be controlled to an optimum value in accordance with the objectof filtering.

INDUSTRIAL APPLICABILITY

[0059] The water treatment device of the present invention can beutilized for filtering various kinds of floating substance in raw watersuch as underground water, river water, lake water, water flowing fromfarm and mountain, including treating water soluble substance such asiron and manganese in such raw water by oxidizing them and making theminsoluble in water and thereupon filtering them. The water treatmentdevice can also be utilized for treating turbid water such as watercontaining red soil and various types of dirty water without usingchemicals.

1. A water treatment device comprising: a raw water supply tube; one ormore jet nozzles, each being at one end portion thereof in communicationwith the raw water supply tube and having at the other end portionthereof a raw water jetting outlet for blowing out the raw water in ajet stream; one or more air introducing tubes provided in correspondenceto said jet nozzle or jet nozzles, each being at one end portion thereofopened to the atmosphere and being at the other end portion thereofopened to the inside of a corresponding one of the jet nozzles upstreamof the raw water jetting outlet; a filter container containing a filterlayer having an upper surface thereof being provided below the jetnozzles with a predetermined interval from the raw water jetting outletsof the jet nozzles; and a filtered water outlet provided in the filtercontainer for taking out water which has been filtered through thefilter layer.
 2. A water treatment device as defined in claim 1 furthercomprising means for reciprocating the raw water supply tube in a planeparallel to the surface of the filter layer.
 3. A water treatment deviceas defined in claim 1 further comprising a baffle plate provided betweenthe raw water jetting outlets of the jet nozzles and the surface of thefilter layer.
 4. A water treatment device as defined in claim 1 furthercomprising: a filter layer support made of a plate screen provided atthe bottom of the filter layer for supporting the filter layer; areverse washing tube provided under the filter layer support for reversewashing the filter layer; and a reverse washing water outlet provided inthe filter container.
 5. A water treatment device comprising: a rawwater supply tube; one or more jet nozzles, each being at one endportion thereof in communication with the raw water supply tube andhaving at the other end portion thereof a raw water jetting outlet forblowing out the raw water in a jet stream; one or more gas introducingtubes provided in correspondence to said jet nozzle or jet nozzles, eachbeing at one end portion thereof connected to a gas supply source andbeing at the other end portion thereof opened to the inside of acorresponding one of the jet nozzles upstream of the raw water jettingoutlet; a filter container containing a filter layer having an uppersurface thereof being provided below the jet nozzles with apredetermined interval from the raw water jetting outlets of the jetnozzles; and a filtered water outlet provided in the filter containerfor taking out water which has been filtered through the filter layer.6. A water treatment device as defined in claim 5 further comprisingmeans for reciprocating the raw water supply tube in a plane parallel tothe surface of the filter layer.
 7. A water treatment device as definedin claim 5 further comprising a baffle plate provided between the rawwater jetting outlets of the jet nozzles and the surface of the filterlayer.
 8. A water treatment device as defined in claim 5 furthercomprising: a filter layer support made of a plate screen provided atthe bottom of the filter layer for supporting the filter layer; areverse washing tube provided under the filter layer support for reversewashing the filter layer; and a reverse washing water outlet provided inthe filter container.